The present invention generally relates to electrohydraulic devices and more particularly relates to electrohydraulic devices used in electronic driving dynamics control systems.
An increasing number of automotive vehicles are equipped with electronically controlled active braking devices and/or electronic systems for driving dynamics control such as ABS, ABS plus, TCS, or ESP. Besides electromagnetically controlled hydraulic valves, the mechanic part of the brake pressure controller also typically includes an electrically driven hydraulic pump for producing brake pressure.
DE-A-41 42 993 discloses an electric machine for converting electric and mechanic energy, which is appropriate for use as a pump motor for an anti-lock system. FIG. 1 illustrated therein shows a cross-sectional view of an electric motor adapted to be connected to a radial piston pump. The electric motor is operated by direct current and includes a commutator with two carbon brushes in addition to stator, rotor, armature windings, etc. A vibration damping element on the shaft of the rotor renders the operation to the pump reduced in noise.
Extreme demands in terms of power density, reliability, low cost, ease of servicing, and low noise levels are placed on electromagnetic transducers for anti-lock systems. Consequently, there is a continuing requirement for more efficient hydraulic pumps.
Particularly high demands are placed in terms of the continuous duty operation of a hydraulic pump and on electromagnetic transducers connected to the pump, especially as it relates to more recent electrohydraulic brake systems (EHB). Electromagnetic transducers do not provide the desired properties, or offer them to an insufficient degree only.
Therefore, the present invention discloses a device which is improved with respect to the actuation of the pump motor compared to prior art hydraulic pumps.
The invention device in an electronic driving dynamics control system, comprising an electromechanic transducer, especially an electric motor, a hydraulic pump, and an electric actuating unit for the transducer, the said transducer including a magnetic or magnetizable stator and a rotor, as well as connections for connecting the actuating unit, and a commutation device for the actuation of electromagnetic windings of the rotor. The commutation device includes three or more commutating elements that are electrically connected to the respective connections so that the windings of the rotor can be actuated individually by the actuating unit, with at least one commutating element being connected to a change-over element that provides for an additional connection for coupling to a rotational speed measurement device.
The electronic driving dynamics control system may e.g. concern so-called ABS, ABSplus, TCS or ESP systems, in particular those systems being advantageously equipped with a device of the present invention which are used within an electrohydraulic brake system (EHB).
The transducer includes a magnetic or magnetizable stator and a rotor, as well as connections for connecting the actuating unit and a commutation device for the actuation of electromagnetic windings of the rotor. According to the present invention, the commutation device includes two or more commutating elements that are electrically connected to the respective connections so that the windings of the rotor can be actuated individually by the actuating unit. At least one of the commutating elements is connected to a change-over element according to this invention. This provides for an additional connection for connecting a rotational speed measurement device.
The commutation device according to the present invention permits the separate electric actuation of the windings in the rotor. It is possible to use this separate electric actuation feature to adjust the characteristic curve of the electromagnetic transducers in a simple fashion, e.g. electronically controlled, to the desired requirements. Noise reduction is achieved at a lower rate of rotational speed. However, the maximum rate of delivery may be achieved in full-load operation.
Starting current peaks may suitably be reduced by switching on of the motor only with the aid of one of the switch selected brushes.
The commutation device is e.g. an arrangement of carbons guided in cages and being pressed with spring elements against a contact in the area of the rotor shaft. Commutation devices for d-c motors with a corresponding design are per se known.
Preferably, the commutation device comprises four commutating elements for the actuation of other windings of the rotor. Not least for redundancy reasons even five or more commutating elements may be advisable to satisfy defined requirements for a more precise adaption of the characteristic curve of the motor.
Therefore, the present invention also relates to a system for controlling brakes in automotive vehicles with at least two redundant system elements (such as an electronic/hydraulic brake controller of double provision or partly provided components of brake controllers) which is characterized in that a first winding of the transducer of this invention is a component of a first system element, and another winding of the transducer is a component of another system element which is designed redundantly to the first system element. If, for example, a winding of the motor in the first system element fails, the other system element is able to actuate the additionally provided second winding.
The actuating unit may be a conventional voltage supply with at least four outputs in the simplest case.
Most favorably, the actuating unit comprises a clock generator for the pulsed and/or clocked actuation of the windings. This permits controlling the delivery rate of the pump with a particularly high resolution. An especially simple rotational speed control may be achieved by using a two-step action controller.
In a particularly advantageous manner, the change-over element and the speed measurement device are integrated into the actuating unit. This is a favorable economy of electronic components.
It is particularly favorable that the device of the present invention may be derived from generic devices known in the art by making modifications. Therefore, the invention concept permits being integrated in a particularly simple fashion into an existing large-scale production of anti-lock systems such as ABS, TCS, or ESP.
The device of the present invention will be explained in detail in the following by way of an embodiment illustrated in the accompanying drawing of a Figure.